Mudpuppies are large aquatic salamanders found in the eastern United States and Canada. Belonging to the family Proteidae, the
genus Necturus currently consists of 5 species. Mudpuppies are often
confused with axolotls (Ambystoma mexicanum), sirens (Siren spp.)
or with larval tiger salamanders (primarily Ambystoma mavortium), which
are also known as waterdogs. Mudpuppies are easily distinguished from other
aquatic salamanders, as they possess 4 toes on the hind feet, whereas most
other salamanders possess 5. The different species of Necturus differ
greatly in size, with the largest (N. maculosus) reaching lengths up to
49 cm (19 in), and the smallest (N. punctatus) maturing at 11.5-19 cm
(4.5-7.5 in) (Petranka, 1998).

Necturus maculosus are generally dark colored, ranging
through a number of shades of brown to black. Typically, they exhibit dark
spots on a lighter background, though this is not always the case. The venter
is lighter in color, ranging from light brown to white or yellow. N. m.
louisianensis have a light yellowish brown to tan dorsum (Petranka, 1998).
Gills are bushy and red. All four limbs are fully functional and are not
reduced like those of sirens or amphiumas. All four feet have four toes. The
tail is laterally compressed and rounded and well adapted for swimming.
However, they often use their legs for locomotion, walking slowly along the
bottom. Necturus have a large, stout body with a wide, flattened head.
The head has two small eyes, usually with a dark stripe extending across them.
Juveniles are smaller, and exhibit light-colored stripes down the entire length
of the body; in most species, these stripes are lost at maturity.

Unless otherwise
stated, all further references to Necturus refer to N. maculosus. Care for other species is similar.

N. m. maculosus

N. m. maculosus

Natural Range and Habitat

N. maculosus are found in most states in the eastern
half of the United States.
Their range extends into the southern parts of the eastern Canadian provinces.
There are two subspecies: N. m. maculosus in the north, and N. m.
lousianensis in the southwestern portion of the range (most of Arkansas and parts of the surrounding states).

Necturus live in rivers, lakes, and other
permanent water sources. One study suggests that they prefer water depth ranges
of 21-35 cm (8-14 in) and 86-95 cm (34-37 in) (Sajdak, 1982). However, they are
frequently found at other depths and have been found as deep as 27 m (88 ft).
They prefer hard cover such as rocks, logs, and overhangs, but will also
utilize debris, reeds, mud, stream banks, and other areas.

Necturus generally remain inactive throughout the
summer. It is believed that they migrate to deeper waters where the water is
cooler. There is speculation in the literature that Necturus may aestivate
(Viosca 1937); however, this has not been proven either way. It is possible
that Necturus simply seeks cooler waters and reduces activity during
these periods as opposed to entering into a true aestivation. Necturus are most
frequently observed in the colder months of the year, when water temperatures
drop below 20°C (68°F). During this time, they may move as much as 1 km (0.6
miles) in a 24-hour period (Sajdak, 1982). They are nocturnal in nature, but
may be more active during the day in deeper or muddy waters where the light
levels are reduced.

N. m. maculosus

N. m. maculosus

Housing

One N. maculosus
can be kept in a 20-gallon long (75x30x30 cm) or larger aquarium. Housing
larger individuals or multiple adults together will require a larger space to
prevent stress. They are territorial, and will fight if sufficient space and
cover is unavailable. Territorial behaviors have been observed between two
individuals housed in a 75-gallon (280-liter) tank, and subsequent fighting
resulted in the ultimate separation of the individuals. Multiple cover objects
should be provided. These may be pieces of driftwood, flowerpots, boards,
rocks, or other objects, but make sure that the objects are free of chemicals,
and lack sharp edges. Boards, driftwood, branches and/or logs from pine or
cedar trees should be avoided due to the risk of poisoning from terpenes and
other chemicals contained in the sap. Personal observations suggest that the
animals prefer large flat rocks, especially when propped against another rock
to create a cave-like area; these caves can be oriented toward the glass to
make it easier to view the animal. Take care to ensure that the cover object
cannot fall and injure the animal or break the glass of the aquarium should any
rocks be disturbed. Mudpuppies themselves can move small rocks around easily.
It is best to include two or three hiding spots per animal to allow each one to
select a favorite spot.

Should an individual
feel threatened, it will keep its gills close to its body. Defense of its own
hiding spot generally consists of vigorous tail fanning across the entrance.
Should another animal try to gain entrance, the resident mudpuppy may bite the
intruder. If this kind of behavior is frequently observed in a multi-animal
enclosure, separation or redesign of the aquarium is warranted.

Unlike many aquatic
salamanders, N. maculosus can tolerate mild currents generated by
filters. Current may even prove beneficial in creating a more natural
stream-like environment. Mudpuppies can jump out of the enclosure, so a lid is
required, unless the top of the enclosure is 10 cm or more above the water
level. A screen lid is recommended, as the ventilation and evaporation can help
reduce water temperature.

N. maculosus prefer temperatures below 20°C (68°F).
In the winter, any temperature between 5 and 20°C (41-68°F) should be fine,
though temperatures on the lower end of this range are strongly recommended.
Summer temperatures should not exceed 22°C (72°F) for long periods of time.
Anything over 25°C (77°F) may prove fatal. N. m. lousianensis may prove
more tolerant of slightly higher temperatures than the northern race.

Stress on the animal
should be kept to a minimum, as stressed animals are more likely to acquire
fungal infection of the gills, which is usually fatal if untreated (personal
observation). Many Necturus obtained from biological supply warehouses
and similar commercial organizations perish from this sort of infection.
Treatment usually involves the use of salt baths and/or medications and may
require the assistance of a veterinarian. Gill size should also be monitored,
as smaller gills may also signal an illness. No Necturus species undergoes
metamorphosis, so gills will not shrink for this reason. Monitor gill size
before attempting treatment, since size may fluctuate over time, or due to
changes in water temperature and/or dissolved oxygen level.

N. m. louisianensis

N. m. louisianensis

Feeding

In the wild, N. maculosus generally eat crustaceans, insects, fish, annelids, mollusks, and
amphibians (Petranka, 1998). In captivity, food items such as scuds
(amphipods), aquatic insect larvae, snails, and worms are readily accepted.
Crayfish are reported to be an important food item in the wild; however, in my
own experience, live crayfish have been ignored. Fish to be used as feeders may
be collected (check appropriate state regulations) or purchased from a pet
store or supermarket. When purchasing fish for use as feeders, avoid using
goldfish, as these are high in saturated fats. Preferably use livebearers,
marine, or cold/cool water fish such as shiners, or rosy reds (a.k.a. fat-head
minnows), as these are much lower in saturated fats and can contain beneficial
polyunsaturated fats. To minimize the risk of disease transmission from fish, a
few simple steps may be followed. The fish may be quarantined for 30 days and
observed for parasites or external lesions, you may breed your own fish, and/or
the fish can be frozen for two weeks or more to eliminate parasitic worms.
However it should be noted that any collected food item(s) including earthworms
or other annelids that are not frozen for at least two weeks prior to feeding
could potentially transmit parasites. It should also be noted that freezing
does not reduce the risk of the transmission of bacterial, viral, or fungal
pathogens.

Quantity of food is
dependent on frequency of feeding. For one adult, 3 large minnows or night crawlers
2-3 times a week is sufficient, adjusting for the size of the animal. A 12-inch
(30 cm) adult can eat as many as 8 medium-sized minnows in a single feeding.
The feeding schedule is very flexible; mudpuppies are adapted to long periods
of time in the wild without food, and can maintain large fat reserves in order
to survive. Adults may live for more than a month with very little food if the
water temperature is cold. Personal observation has shown that feedings should
be increased when the tail appears to be thinning.

Necturus will learn to take food from a keeper’s
hand, but care must be taken to avoid being bitten. To hand-feed, approach the
animal slowly, and allow it to feed on its own terms. With patience, this can
be one of the more rewarding aspects of keeping the species. Mudpuppies rarely
bite, and a feeding accident is the most likely time for a bite to occur. Bites
rarely break the skin, but can be painful. Teeth are designed for holding prey,
not tearing, and food items are swallowed whole.

N. m. louisianensis juvenile.

N. m. louisianensis subadult.

Reproduction

N. maculosus mate in the fall/winter and lay eggs in
the spring. Most populations deposit in late May to early June, though it may
be as early as late April. Females construct nests on the underside of a cover
object, and usually remain there until they hatch. It is unknown whether the
female actively guards them, or merely continues to occupy the location.
Regardless, the female’s presence protects the eggs from predators such as fish
or crayfish, and other mudpuppies. Females lay up to 12 eggs per day, in a
single layer 15-30 cm (6-12 in) in diameter (Petranka 1998). Eggs are 5-6.5 mm
(1/4 in) in diameter, and have three envelopes, with the outermost jelly coat
allowing the eggs to adhere to the underside of the cover object. Clutch sizes
vary, but are generally in the range of 60-100 eggs. Fertilization is internal,
and sperm is retained for several months. Many other details about reproduction
in this species are currently unknown.

Larvae hatch in July or
August, after an estimated incubation period of 38-63 days. Larvae are much
more colorful than adults, featuring a brown stripe lengthwise on a light body.
They grow an average of 56 mm (2 in) per year in the wild, reaching maturity at
20 cm (8 in) total length, after approximately 5 years.

Gender in N.
maculosus can be determined by examining the vent of the animal. During the
breeding season, males will have a swollen cloaca, as well as a pair of
nipple-like papillae at the rear of the vent (Sajdak, 1982). Additionally, the male vent has a crescent-shaped transverse groove. Females may have
lighter coloration around the vent.

N. m. maculosus male vent. Note that the vent is more crescent shaped than the female, and the two papillae (small nubs) are visible at the lower end of the vent.

N. m. maculosus female vent.

To date, there have
been few reported captive breeding successes. The reasons for this may include
their scarcity in captivity and the tank size requirements for keeping multiple
animals together. A keeper wishing to attempt breeding should slowly begin
decreasing the water temperature to around 15°C (59°F) or colder in the fall,
and maintain this temperature until spring. It may be beneficial to manipulate
the photoperiod in conjunction with temperature to maximize the chances of
reproduction, but bright or intense lighting should be avoided as it may
increase the stress on the animal. A strong current may be useful or even
necessary; they are frequently observed downstream of dams in the wild trying
to move upstream, so current orientation may play a role in the location of
nesting sites and attraction of mates. Finally, introduction of unfamiliar
animals at this time may also increase the chances of breeding.

N. m. maculosus egg clutch.

Juvenile N. m. maculosus specimen from Michigan.

Should breeding prove
successful, it may be wise to remove all animals except for the nesting female
from the enclosure, as adults have been known to cannibalize eggs. It is
unknown if females will eat their own eggs. Despite this, leaving the eggs
with the female may prove most successful; in almost all nesting caudate
species studied to date, the removal of the female usually results in loss of
many eggs to fungal infections. Artificial rearing of eggs is a labor-intensive
method that requires the separation of the eggs into small groups, which are
then monitored and agitated as if the female was attending the clutch. The
highest artificial hatch rates have been obtained by the use of hatchers of the
kind used by trout hatcheries (Vess, Harris; 1997). If a non-intrusive method
of observation is possible, careful monitoring of the eggs and female may allow
the keeper to salvage a nest if predation does occur.

One successful captive breeding has been reported (Raffaelli 2000). A group of 2:2 adults was housed in a tank 1.7 x 0.8 meters (5 x 2.6 feet) with a current. The temperature was cycled between 6°C in winter and 16°C in summer. A nuptial dance was observed in March, and eggs were found in May. Most of the eggs were lost to fungus, but best success was achieved for eggs left together with the female.

Captive N. m. maculosus with eggs.

N. m. maculosus eggs laid in captivity.

Conservation and Ecology

N. maculosus are abundant in many states. Specific
populations may become threatened or extirpated due to siltation and/or
pollution. They are considered threatened in Iowa, Indiana, Virginia, and Vermont, and vulnerable in Oklahoma. They are considered endangered in Georgia and Maryland. They may have been extirpated from South Dakota and North Carolina (NatureServe Explorer, 2004). Suitable
habitat is decreasing in some areas, and other populations may begin declining
in the future.

One major problem for Necturus
is the lampricide, TFM. Areas experiencing problems with sea lampreys, which
are a pest to the fishing industry, employ TFM to selectively kill lamprey
larvae. Unfortunately, it also kills mudpuppies and other larval amphibians.
In some areas treated with this chemical, populations have dropped drastically
(Schmitt, 2004); however, the lampricide is unlikely to be solely responsible,
as studies have shown that a dose exists that is lethal to lampreys but has
limited effect on mudpuppies (Christie, 2000). All mudpuppies currently sold
for pets or research are wild caught. They are used extensively for medical
training and research. It is possible that commercial collecting may have an
unsustainable impact on wild populations, especially in areas already under
pressure from other threats.

N. maculosus is the only host of the salamander
mussel. The salamander mussel uses the mudpuppy as a host during the mussel’s
larval stage. The mussel larvae attach themselves to the mudpuppy’s gills, and
drop off after metamorphosis (Michigan Natural Features Inventory, 2002). The
relationship between the parasite and the host has not been extensively
studied, but it is unlikely that the mussel kills the host animal. The
salamander mussel is the only freshwater mussel that uses a non-fish host. This
mussel is threatened or endangered in several states, and should Necturus
become extirpated from an area, the mussel will likely follow, as the absence
of mudpuppies will prevent successful reproduction of the mussel.

Predation of adult N.
maculosus is rarely observed, though fish, turtles, and northern water
snakes (Nerodia sipedon) have been documented as predators (Petranka,
1998). Adult mortality is presumably low and primarily attributed to human
interference. Fishermen frequently catch them, and many times will leave them
on the ice or on the shore, due to misconceptions about their predation of fish
and fish eggs, the false belief that they are poisonous, or simply because of
their general appearance. Little literature exists to document predation on
young Necturus, but it can be assumed that fish, crayfish, wading birds,
and other organisms eat them.